The heat-resistant temperature of a chlorinated vinyl chloride resin becomes higher than that of a vinyl chloride resin due to chlorination. Therefore, the chlorinated vinyl chloride resin has been used in various fields such as a heat-resistant pipe, a heat-resistant industrial plate, a heat-resistant film, and a heat-resistant sheet.
The chlorinated vinyl chloride resin generally is produced by chlorinating a vinyl chloride resin while supplying chlorine to an aqueous suspension obtained by suspending vinyl chloride resin particles in an aqueous medium. Usually, when chlorination is performed by photochlorination, the irradiation of ultraviolet light is carried out through use of a mercury lamp so as to generate a chlorine radical (Patent document 1).